1. Field of the Invention
The present invention relates to a method for the esterification of fatty acids and/or fatty acids contained in fats and oils with lower monovalent alcohols, especially methanol, whereby the fatty acids with strong mineral acids, such as sulphuric acid, dissolved in lower alcohols, especially in methanol and/or exclusively in the lower alcohols, especially in methanol, are compounded with acid ion exchanger resins. Furthermore, the invention relates to a system for the implementation of the method.
2. Discussion of Background Information
From textbooks for organic-preparatory chemistry, such as “Organikum”, 13th ed., 1974 page 441 et seq. or Weygand/Hilgetag, ,,Organisch-Chemische Experimentierkunst, 4th ed., 1970, page 377 et seq., it is known that carboxylic acid esters or fatty acid esters may be esterified by esterification of the free acids with lower alcohols, preferably at the temperature of ebullition of the alcohols in presence of strong acids, such as hydrogen chloride, sulphuric acid or sulphonic acids.
A method for the esterification of a fatty acid/fatty acid ester mixture, isolated from the “glycerine phase”, is described in EP 708 813 A, whereby the free fatty acids obtained from the neutralization of the “glycerine phase” are heated to a temperature of 85° C. for two hours, with methanol and concentrated sulphuric acid acting as a catalyst, whereby the content of free fatty acids decreases from about 50% to 12.5% and the entire mixture is supplied without any further treatment to an alkali-catalyzed transesterification and the catalyst acid is exported through the transesterification process.
Further methods for esterification of free fatty acids are described in EP 127 104 A, EP 184 740 A and U.S. Pat. No. 4,164,506, whereby the free fatty acids are present in a mixture with fatty acid triglycerides and the esterification is carried out by heating with methanol at 65° C., whereby sulphuric acid or a sulphonic acid act as a catalyst.
Furthermore, a method and a device for the production of carboxylic acid ester are known from WO 90/08127 A, whereby the esterification is carried out in a counterflow reaction column. The carboxylic acid to be esterified is introduced into the counterflow reaction column from above and alcohol, in particular methanol, is introduced from below in vapour form. The mixture is practically circulated for esterification. Several plates with ion exchangers are arranged in the column, the carboxylic acid reacts with the alcohol in the esterification zones. The water which is produced during esterification is removed with the methanol vapour during the esterification process at the upper end of the column, while the ester is removed at the lower end of the column.
Moreover, a method for the catalytic or non-catalytic esterification of acids is known from U.S. Pat. No. 5,324,853. In the course of the method, the reaction mixture is heated in a container with several stirring devices, so that the water that is produced is removed in vapour form during the esterification process.
In U.S. Pat. No. 5,945,529, a transesterification process based on the counterflow principle and using an inert gas is described. In the method, the lower alcohol that is produced during the transesterification is removed by a strip gas during the process. The transesterification is carried out by a multistage column or a multistage counterflow reactor.
An esterification of unsaturated carboxylic acids is known from EP 0 713 857 A1. Here, the water, produced by the esterification, is extracted from the various esterification zones containing ion exchangers during the process with the help of a medium in vapour form. During the process, the vapours are withdrawn and the reaction water is removed from the cycle. The reaction vessel that is used for such purpose has a fixed bed with 1 to 10 stages. Each stage is comprised of a filter- and catalyst bed.
From the citation index of the WPI database, section Ch, week 199818, XP 00251804 a horizontal tank with stirring devices is known, wherein vapour is withdrawn during the process in order to extract water that is produced.
In conclusion, WO 02/38529 A is referred to. In this publication, a method for the production of fatty acid esters of lower alcohols is described, wherein by neutralization of the glycerine phase and by a subsequent esterification with an acid, a diesel substitute fuel is produced.
The serious disadvantage of all these known methods lies in the fact, however, that the esterification step requires an enormous amount of time. Thus, as a rule the kind of esterification requires stirring over a period of two to three hours.